Curing of silicone gel compositions produces silicone gels with excellent electric, heat-resistant, weather-proof, and stress-relaxation properties. Therefore, such compositions find application as sealants, cushioning agents, shock-absorbing agents, or fillers for electric and electronic components. An example of such silicone gel compositions is a composition comprising a branch-chained organopolysiloxane having a molecular terminal capped with a silicon-bonded vinyl group, a diorganopolysiloxane having both molecular terminals capped with silicon-bonded vinyl groups, an organopolysiloxane having silicon-bonded hydrogen atoms, and a platinum catalyst (see Japanese Laid-Open Patent Application [Kokai] Sho 62-181,357).
However, the aforementioned silicone gel composition does not possess thixotropic properties and has a tendency to spreading out during application. Therefore, when this composition is used for sealing some electric and electronic components, it may [accidentally] seal other electric and electronic components for which sealing is undesirable.
On the other hand, silicone gel compositions with thixotropic properties are known. Examples of such compositions are a silicone gel composition comprising an organopolysiloxane having a silicon-bonded vinyl group on a molecular terminal and a 3,3,3-trifluopropyl group in a side molecular chain, an organopolysiloxane having a silicon-bonded hydrogen atom on a molecular terminal and/or in a side molecular chain and a 3,3,3,3-trifluoropropyl group in a side molecular chain, a platinum-type catalyst, and a hydrophobized silica (see Japanese Laid-Open Patent Application [Kokai] HEI-7-324,165) and a two-liquid type silicone gel composition comprising the following components in a mixed state: an organopolysiloxane having at least two silicon-bonded alkenyl groups in one molecule, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, an inorganic filler, an organopolysiloxane having a silicon-bonded alkoxy group, and a platinum-type catalyst (see Japanese Laid-Open Patent Application [Kokai] HEI-9-132,718).
However, after application onto the surfaces of electric or electronic devices, these silicone gel compositions with thixotropic properties spread out over the surface when cured by heat and seal the areas of the electric or electronic device which are not supposed to be sealed. Furthermore, the silicone gels obtained as a result of curing the aforementioned compositions have poor resistance to cold temperatures. For example, they rapidly loose their gel-like state at such low temperatures as -40.degree. C. and thus lead to breakage in conductive patterns or to cracking in soldered areas.